food biotechnology notes

SUBJECT: FOOD BIOTECHNOLOGY FACULTY: Dr. V. Krishna Murthy

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UNIT 1 -SCOPE AND RELEVANCE FACULTY- Dr. V. Krishna Murthy SAP- Meha Jabin SEM: 7

LECTURE 1: Introduction, scope and constituents of food substances.

History of Food Microbiology In 1665, Robert Hooke published Micrographia that included the structure

of Mucor, a genus of fungus. In 1676, Antony van Leeuwenhoek used a crude microscope to study pond

water. 1861: Louis Pasteur demonstrated that microorganisms are present in the air with his S-shaped flask – disproving spontaneous generation. Commonly called the “Father of Microbiology”. Showed that microbes are responsible for fermentation. Fermentation is the conversion of sugar to alcohol to make beer and wine.

1876: Robert Koch Provided proof that a bacterium, Bacillus anthracis, causes anthrax. Developed Koch’s postulates, which are used to prove that a specific

microbe causes a specific disease. Modern Contributions Many foodborne pathogens were discovered in the early to mid 20th century. Bacteria: Salmonella species, Clostridium botulinum, Staphylococcus

aureus, Bacillus cereus Viruses were first crystallized and associated with disease in the 1930s. James Watson and Francis Crick discovered the structure of DNA in the

middle of the 20th century. This led to a better understanding of microbes and how they cause illness,

how we can detect them, how we can use them in industry. Molecular biology is vital to food microbiology. GMPs (Good Manufacturing Practices) provide manufacturers with

procedures that yield safe products. HACCP (Hazard Analysis Critical Control Point) plans help to assure safety

at each key step of the manufacturing process.


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Food irradiation is approved as “kill” step in the processing of raw poultry and meat.

About 1/3 of the world’s food supply is lost to spoilage. The world is demanding safer food. “Globalization” of the food supply can cause problems with sanitation

standards. The causes of ½ of food-borne illness cases are unknown (over 90% of

bacteria remain undiscovered. Introduction: Food science is a study concerned with all technical aspects of food, beginning with harvesting or slaughtering, and ending with its cooking and consumption, an ideology commonly referred to as "from field to fork". It is considered one of the life sciences and is usually considered distinct from the field of nutrition. Food science is a systematic study of the nature of food materials and the scientific principles underlying their modification, preservation & spoilage. Food science – PCMB, Biochemistry, Microbiology, & food technology – necessary to prepare, package, store and serve wholesome, high quality food products. Important Developments in Food Science: (1)Food preservation. (2) Food spoilage. (3) Food intoxication. 1)Food Preservation: a)Canning b)Chemical c)Brine Bath d)Freezing A. Kircher, a monk (1950’s) boiled cans containing food in water bath for varied periods to kill “worms” and to slow spoilage.

SO2 smoking. Burn special wood which release ketones, aldehydes and pyrogenic flavourants. Hence spoilage is slowed down

Retain succulence of food pulps, also add taste and extend keeping time. (0.3% NaCl and 3% sucrose)

Freezing: 0 degree and sub 0 degree preservation. Freeze drying:Lyophilization Refrigeration:Refrigeration at 4 – 18 degrees c.


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and food also gets a flavour.

e) Steam f) Natural g) Radiation h)Controlled/Modified Atmospheric Storage (C/MAS):

Steam sterilization done by autoclaving. For different foods different time-temp combinations are required to prevent caramelization, melad browning, saltprecipita-tion, sugar reactions with amino acids, such that food constituents should not be affected. Hence retain the palatability of food and quality of food.

Drying by sun and evaporation.

irradiation of foods, cold pasteurization or cold sterilization (radiorization). non-ionizing radiations like UV alter DNA ionizing radiations like x, alpha, beta and gamma rays trigger the release of electrons from chemicals.

Storage rooms are made oxygen free and 5% carbon dioxide atmosphere is maintained to prevent aerobes from growing.

(2) Food spoilage: Food borne infection: are caused by viable pathogenic

bacteria. (3) Food intoxication: is caused due to release of toxins by bacteria growing on

food (exotoxins), botulin, cholera toxin etc. Scope:


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Sub-disciplines - Food Chemistry / Food Microbiology / Food Processing

HACCP- Hazard Analysis Critical Control Point: Each point depicted above is a control point and quality assurance is done at every point. It is different from quality control where the products are checked only in the end. Food safety The causes, prevention and communication dealing with food-

borne illness. Food microbiol. The positive and negative interactions between micro-

organisms and foods. Food preservation

The causes and prevention of quality degradation.

Food engineering The industrial processes used to manufacture food. Product development

The invention of new food products.

Sensory analysis The study of how food is perceived by the consumer's senses.

Food chemistry The molecular composition of food and the involvement of these molecules in chemical reactions.

Food packaging The study of how packaging is used to preserve food after it has been processed and contain it through distribution.

Molecular gastronomy

The scientific investigation of processes in cooking, social & artistic gastronomical phenomena.

Food technology The technological aspects. Food physics The physical aspects of foods (such as viscosity, creaminess,

and texture). Constituents of Food: Basic food chemistry deals with the three primary components in food: carbohydrates, lipids and proteins. Carbohydrates make up a group of chemical compounds found in plant and animal cells.

They have an empirical formula CnH2nOn or (CH2O)n. Since this formula isessentially a combination of carbon and water these materials are called “hydrates ofcarbon or carbohydrates”.

Carbohydrates are the primary product of plant photosynthesis, and are consumed as fuel by plants and animals.


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Food carbohydrates include the simple carbohydrates (sugars) and complex carbohydrates (starches and fiber).

Proteins are important components of food.

Every cell requires protein for structure and function. Proteins are complex polymers composed of amino acids. (There are 20

amino acids found in the body. Eight of these are essential for adults and children, and nine are essential for infants).

Essential means that we cannot synthesize them in large enough quantities for growth and repair of our bodies, and therefore, they must be included in our diet.

Proteins consist of long chains of 100-500 amino acids that form into three-dimensional structures, their native state. When the native state of the protein is changed, there will be a change in the three-dimensional structure, which is referred to as denaturation.

Factors that cause denaturation include heating, acid, beating and freezing. Lipidsinclude fats, oils, waxes, and cholesterol. In the body, fat serves as a source of energy, a thermal insulator, and a cushion around organs; and it is an important component of the cell.

Fats have 2.25 times the energy content of carbohydrates and proteins, most people try to limit their intake of dietary fat to avoid becoming overweight.

In most instances, fats are from animal products – meats, milk products, eggs, and seafood and oils are from plants – nuts, olives, and seeds.

Lipids are used for flavor, to cook foods, and to improve the texture of foods.

Along with carbohydrates, proteins and fats, minerals, vitamins, organic acids, pigments, enzymes, flavoring agents and other organic substances are present in varying amounts in foods. These constituents attribute food in their structure, texture, color, flavor and nutritive value.To a consumer the physical appearance is as important as its chemical composition. LECTURE 2: Colloidal systems in food, stability of colloidal system.

Classification of food based on particle size: 1) True Solutions:

Has two parts, Solute dissolved in solvent. Ions of molecules are <1 micron (10-4cm).


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They are further sub classified into- (a) Saturated solution (b) Unsaturated solution and (c) Supersaturated solution.

2) Coarse Suspensions:

Dispersion of coarse particles in liquid. Particle size is > 1 micrometer and the particles tend to settle down if not

agitated. 3) Colloidal Dispersion/System:

The particle size is in between coarse suspensions and true solutions. Colloidal particles are non-crystalline and ultra-micro in size. (0.001µm-

1µm). They impart features to food and do not separate out upon standing.

Colloidal systems give structure, texture and mouth-feel to many different products, for example: Jam, Ice-cream, and Mayonnaise. Colloids are formed when one substance is dispersed through another, but does not combine to form a solution. There are many types of colloidal systems depending on the state of the two substances mixed together. Gels, sols, foams (e.g. egg white foam) and emulsions (e.g. butter) are all types of colloids. The substance which is dispersed is known as the disperse phase and is suspended in the continuous phase. Egg white foam is an example of this. Air bubbles (disperse phase) are trapped in the egg white (continuous phase) resulting in a foam. Stability of Colloidal System depends on two factors:

1. The charge on the colloidal particle – As the surface charges on the colloidal particle are similar, like charges repel and the particles do not get attracted or join together (stable); when the charge is neutralised, the colloidal particles flocculate and separate out.


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2. A layer of water that is tightly bound on the molecule- Part of water present in food use free water that can act as solvent and has flow properties; the rest of water is bound (with starch or protein) with food by hydrogen bonding and influences physical properties. Many colloidal systems are hydrophilic in nature and attract a layer of water that acts as insulation and keep system stable.

Instability of colloidal system: Most colloids are stable, but the two phases may separate over a period of time

because of an increase in temperature or by physical force. They may also become unstable when frozen or heated, especially if they

contain an emulsion of fat and water. Types of colloidal systems in food: Sols, Gels, Emulsions and Foams. SOLS A sol is a liquid colloid or mixture in which solid particles are dispersed in a

liquid phase (solid /colloid particles=dispersed phase; liquid=continuous phase). The dispersed phase is attracted to molecules of the continuous phase.

Viscosity of sols varies – skim milk (flows); tomato ketchup (barely flows);

viscosity depending on concentration of solid and temperature of sol. Irrespective of viscosity, in a sol the solid particles are always distributed and

do not settle. Eg. Proteins in milk (like electric charges in protein on surface repel)

GELS In gels liquid forms the dispersed phase and solid forms continuous phase

(reverse sol). Gels do not flow since the concentration of solid is high. Liquid adsorbed on the surface of the solid molecules and this water gives

structure to the gel. Remaining water is trapped in the three dimensional meshwork of gel.


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Gelling agent may be a polysaccharide (cornflour), protein like albumin in caramel custard, calcium caseinate in curds.

Gums, pectins and gelatin can form gels even at low concentrations. When gels are stored, they shrink and compact in mass, since liquid entrapped

is expelled from interstitial spaces (syneresis or weeping gel) eg: baked custard, moulded desserts, curds.

Sol-Gel:

Are reverse colloidal systems and can be interchanged. Sols when cooled become Gels and when Gels are cooled become Sols.

Sols when converted into gels the energy levels fall. Dissolved gelatin jelly crystals (SOL)Jelly(Gel).

EMULSIONS

When water and oil are shaken together, they form an emulsion.

The dispersed liquid will have larger surface area in emulsion. This emulsion is unstable. If left to stand, the oil will form a separate layer on top of the water.

An emulsion may be:

o Oil-in-water (o/w) in which case small oil droplets are dispersed through water, e.g. milk, or

o Water-in-oil (w/o) in which case small water droplets are dispersed through oil, e.g. butter.

Depending on their stability emulsions are classified into temporary

emulsions, semi-permanent emulsions and permanent emulsions. The two liquids are immiscible (they will not mix together). A stable emulsion is formed when two immiscible liquids are held stable by a third substance, called an emulsifying agent. An emulsifier (also known as an emulgent) is a substance that stabilizes an emulsion by increasing its kinetic stability. One class of emulsifiers is known as surface active substances, or surfactants. Examples of food emulsifiers are egg yolk (where the main emulsifying agent is lecithin), honey etc.


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An emulsifying agent is made up of two parts. One is hydrophilic (water loving) and the other is hydrophobic (water hating). The emulsifier holds the disperse phase within the continuous phase. This results in the emulsion becoming stable.

Factors that affect the stability of emulsions are:

i. Presence of emulsifying agent ii. Concentration of emulsifying agent

iii. Size of droplets iv. Ratio of oil to water

Mayonnaise is an example of a stable emulsion of oil and vinegar, when egg yolk (lecithin) may be used as an emulsifying agent. Stabilisers are often added to emulsions to increase the viscosity of the product. These help improve the stability of the emulsion, as over time the emulsion may separate. Stabilisers also increase shelf life, E461 methylcellulose, used in low fat spreads. Other emulsifiers are glycerol monostearate, steryltartarate and casein. FOAMS: Foams are composed of small bubbles of gas (usually air 1µm) dispersed in a liquid, e.g. egg white foam. As liquid egg white is whisked, air bubbles are incorporated. The mechanical action causes albumen proteins to unfold and form a network (also reduces surface tension), trapping the air.If egg white is heated, protein coagulates and moisture is driven off. This forms solid foam, e.g. a meringue. Ice cream, bread and cake are other examples of solid foams. Liquids that form foam must have low vapour pressure, and low surface tension. Solid particles present increase stability by trapping gases.


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Methods and Ingredients that Influence Degree of Dispersion:

1. Mechanical stress Whipping, agitating, beating, homogenising, etc, increase the rate of dispersion.

2. Increase in temperature Increases the K.E. and hence the dispersion (but some protein coagulate on heating)

3. Addition of acid / alkali Addition of acid to milk coagulates it, whereas addition of alkali to cellulose in presence of pectin hydrolyses the former making the dispersion better.

4. Water Increase in water content increases dispersion 5. Enzymes Renin coagulates casein and hence decreases dispersion. Proteinases hydrolyseglutin protein of wheat and increases dispersion.

LECTURE 3: Types of Food Starches and examplesSoluble Fibers: Pectin, Gums &Mucilages

Starch is the primary carbohydrate source for growing seeds and leaf tissue development and is found in leaves, tubers, fruits and seeds. Starch is acomplex carbohydrate made up of two components, Amylose and Amylopectin. Sources: Roots/Tubers: Potato, Arrowroot, Tapioca, Cereals, Corn, Waxy corn, Wheat, Rice Food Starch Widely used as a food ingredient. A very wide selection of starches, both native and modified Gelation and pasting characteristics altered by other ingredients and process

conditions Starches usually contain more amylopectin than amylose Generally roots/tubers contain more amylopectin than cereals Roots/Tubers: 80% amylopectin Cereals: 75% amylopectin Waxy corn and rice contain virtually all amylopectin Characteristic Amylose Amylopectin Form Essentially Linear Branched Linkage Alpha 1-4 glucosidicbonds

(some alpha1-6) Alpha 1-4; alpha1-6 glucosidic bonds


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Polymer Units 200 to 2000 Upto 20, 000,00 Mol. Wt. <0.5 million 50-500 Gel Formation Firm Non-gelling to soft Classification of starch based on amylase and amylopectin content: 1) Non-waxy starch: 20-30% amylase. 2) Waxy Starch: 100% amylopectin. Cannot form rigid gels only smooth pates are

seen. 3) Hi-amylose content starch: 50% or more amylase.

AMYLOSE AMYLOPECTIN Forms gels No gel formation Good thickening agent

Less useful as a thickening agent

Less molwt More molwt, 4 times that of amylase.

Shapes of starch Granules: Large granular, like mussel shellsPotato Large ellipticalSago Large and small dish shapes Wheat Polygonal Corn Small round or oval Tapioca Small oval Oats Very small polygonal Rice Modified Starches:

Pregelatinized Starch: Thin boiling/Acid modified starch: Cooked till gelatinized Roller dried Water added to the previously

dehydrated starch Allowed to swell to desired thickness

without heating Used in instant pudding mixes, baby

cereals Physical changes is used to modify

Starch is suspended with dilHCl/HNO3 at temperature below gelatinization. - Starch gets hydrolysed and fragmented.

Solubility increases and thickening ability decreases

Hot thin boiling starch are very fluid

Used to make gum drops, easily


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native starch

poured, the film gels on cooling and aging.

Oxidised Starch: Cross linked starch: These are chemically modified thin

boiling starch Treatment with alkali Sodium

Hypochlorite Starch granules are oxidized and forms

soft gel OH groups are oxidized to aldehydes

or acids

OH groups on two different molecules in the same granule are substituted by acetic anhydride.

Greater linking and lesser retrogradation tendency

Used as thickener and stabilizers Control degree of thickness that

causes a stingy taste

Starch phosphates: Starch esterified with Sod. Tripolyphosphate It improves texture and stability Hi clarity Decreased syneresis Hi freeze-thaw stability Properties of starch: Gelation Gelatinized starch mixture is either sol or in gel form when cooled. Gelatinization is the swelling of starch granules by absorption of water

molecules. Heat energy breaks H bonds and facilitates the entry of water molecules. Satrch chains uncoil, size increases and water gets bound to amylose and

amylopectin This mixture is translucent and viscous. Process of swelling of starch grains and formation of viscous starch pastes is

called gelatinization Amylose leaches out from the starch granules. Forms H bonds with other amylase molecules and looses energy as it cools. A 3-D network of amylase is formed. This forma the continuous phase. When starch is transformed ti gel no flow properties are seen. The factors affecting gelation are: type of starch, conc. of starch, duration of

heating, stirring and aging of gel.


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Fibers Functions of Fibers: Water holding capacity Viscosity Cation exchange capacity Bile binding capacity Fermentability Not digested by small intestine enzymes-why? Bacteria-make short chain fatty acids, water, gas. Short chain fatty acids absorbed at large intestine and transported by blood used for energy.

Insoluble Fibers Soluble Fibers Cellulose-bran,vegetables Hemicellulose-bran, whole grains Lignins-fruits, mature vegetables, flax Generally-accelerate gi transit, Increase fecal weight (promotes bowel

movements), Slow starch digestion, Delay glucose absorption

Pectins-apples, carrots, Gums and mucilages- oats, legumes Generally-delay gi transit, Delay glucose absorption, Lower blood cholesterol

But, there can be exceptions Soluble Fibers: Soluble fibres lower cholesterol (bile issue) fibre may displace fat in diet Diabetes: Control weight-diabetes, slow glucose absorption-glucose surge and

rebound associated with diabetes onset


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Cancer: lower colon cancer-maybe by diluting and binding and more rapid excretion of carcinogens (Soluble and Insoluble Fibre)

Gastrointestinal health: Enhance health of gi tract-healthy intestine easier to

block absorption of unwanted constituents (Insoluble fibres) Fibre from natural sources rather than commercially prepared fibre is better

because foods contain vitamins and minerals as well as the fibre. Gums and Mucilages Gums & mucilage have similar constitutions and on hydrolysis yield a mixture of sugars &uronic acids. Gums are considered to be pathological products, while mucilage is formed by normal metabolism.

Gums Soluble Fibers Gums are amorphous translucent substances which are insoluble in alcohol & most organic solvents. It is soluble in water & gives a viscous, sticky solution. Other gums are swollen by absorbing water to form a jelly-like mass. Gums are commonly found in trees & shrubs of a number of Families, especially Leguminosae, Rosaceae, Sterculiaceae, Rutaceae Gums are abnormal products formed by injury, draught by breakdown of cell-walls –extracellular gummation Gum Constituents Gums consist of Ca, Mg & K-salts of

polyuronides. Gums can be hydrolysed by prolonged

Mucilages are generally normal products of metabolism formed within the cell (intracellular formation). Egs.: - Storage material - Water storage reservoir - Protection for germinating seeds. Mucilage is often found in: - Epidermal leaf cells (Senna) - Seed coats (linseeds, psyllium) - Roots (marshmallow) - Barks (Slippery elm) Herbs containing mucilages: Psyllium


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boiling with dilute acids to yield a mixture of sugars and uronic acids.

Sugars = monosaccharides (mainly galactose, arabinose, xylose).

Herbs containing gums:

- Tragacanth gum - Sterculia gum - Acacia gum

LECTURE 4: Protein rich foods, popular oils and fats in foods, pulses, dairy products and vegetable oils.

The protein content is measured in grams of protein per 100 g of an edible portion of food, without referring to the quality of the protein. All proteins are not equally digestible. Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method of evaluating the protein quality based on the amino acid requirements of humans. Our bodies are made up of 75% protein. The Important Role of Protein Rich Foods Proteins have role in human development, growth and muscle healing, helps

body repair and make new cells. Provide a source of energy . Control many of the important metabolism processes in the body. The amount of recommended daily protein rich foods varies with age and gender. Age Grams/day Grams/kilograms/day 1-3 years 13 g/day 1.10 g/kg/day 4-8 19 g/day 0.95 g/kg/day 9-13 34 g/day 0.95 g/kg/day 14-18 Boys Girls

52 g/day 46 g/day

0.85 g/kg/day 0.85 g/kg/day


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Two types of dietary proteins: Complete proteins - contains an almost equal proportion of all nine essential

amino acids which the human body cannot synthesize and must therefore get from food, and are found primarily in the following types of protein rich foods - animal foods such as meat, fish, poultry, eggs, milk, and milk products (yogurt and cheese). Soybeans are the sole plant proteins that also fall in this category.

Incomplete proteins - lack one or more of the essential amino acids needed by

our bodies. They are derived mainly from plant sources such as beans, peas, nuts, seeds, and grains; as well as a small amount are found in vegetables.

Incomplete proteins can be combined with other plant or animal proteins to

form complete proteins. Rice and beans, rice and lentil, idli/ dosa and sambhar, milk and wheat cereal, pasta and cheese and cheese sandwiches are good examples of protein combination's which yield complete protein rich foods.

Protein isolates (absorbable); Concentrates: Enriched or fortified proteins Vegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with

waxes which lack glycerin in their structure. Although many plant parts may yield oil, in commercial practice, oil is

extracted primarily from seeds. Fats and oils also typically contain free fatty acids, monoglycerides and

diglycerides, and unsaponifiable lipids. Culinary Use of Oils and Fats:

The oils serve a number of purposes in this role:

Shortening - to give pastry a crumbly texture. Texture - oils can serve to make other ingredients stick together less. Flavor - while less-flavorful oils command premium prices, some oils, such as

olive, sesame or almond oil, may be chosen specifically for the flavor they impart.

Flavor base - oils can also "carry" flavors of other ingredients, since many flavors are present in chemicals that are soluble in oil.


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Oils can be heated, and used to cook other foods. Oils suitable for this purpose must have a high flash point. Such oils include the major cooking oils - soy, canola, sunflower, safflower, peanut, cottonseed, etc.

Tropical oils, like palm oil and coconut oil, and rice bran oil, are particularly valued in Asian cultures for high temperature cooking, because of their unusually high flash point.

Hydrogenated oils

Unsaturated vegetable fats and oils can be transformed through partial or complete hydrogenation into fats and oils of higher melting point.

The hydrogenation process involves "sparging" the oil at high temperature and pressure with hydrogen in the presence of a catalyst, typically a powdered nickel compound.

Carbon-carbon double-bond is chemically reduced to a single bond; two hydrogen atoms each form single bonds with the two carbon atoms.

The elimination of double bonds by adding hydrogen atoms is called saturation; as the degree of saturation increases, the oil progresses toward being fully hydrogenated.

Oil may be hydrogenated to increase resistance to rancidity (oxidation) or to change its physical characteristics.

As the degree of saturation increases, the oil's viscosity and melting point increase.

Dairy products are generally defined as foods produced from cow's or domestic buffalo's milk. They are usually high-energy-yielding food products. A production plant for such processing is called a dairy or a dairy factory. Most dairy products contain large amounts of saturated fat.

Types of dairy products Milk after optional homogenization, pasteurization, in several grades after standardization of the fat level, and possible addition of bacteria Streptococcus lactis and Leuconostoccitrovorum Cream, Cultured buttermilk, Milk powder, Condensed Milk, Khava, Butter, Cheese, Paneer, Casein, yogurt etc.

Food (Per 100g) Protein Carbs Fat Calories Almond Nuts 21.1g 6.9g 55.8g 2541kJ (614kcal)


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Asparagus 2.9g 2.0g 0.6g 106kJ (25kcal) Baked Beans 9.5g 22.1g 0.4g 130kcal Bananas 1.2g 23.2g 0.3g 426kJ (100kcal) Beef Fillet Steak 20.9g 0g 7.9g 648kJ (155kcal) Bread (whole meal) 11.0g 39.1g 2.2g 935kJ (220kcal)

Broccoli 4.2g 3.2g 0.2g 133kJ (31kcal) Carrots 0.6g 7.9g 0.3g 156kJ (37kcal) Cheese 30.9g 0.1g 15.0g 1085kJ (260kcal) Chicken Breast (Skinless) 23.5g 0g 1.7g 462kJ (109kcal)

Coconut 3.33g 15.23g 33.49g 354 Cod fish 17.9g 0g 0.9g 340kJ (80kcal) Cottage Cheese 12.2g 4.5g 1.5g 340kJ (80kcal) Crab meat 18.1g trace 0.5g 330kJ (80kcal) eggs 12.5g Trace 3.2g 627kJ (151kcal) Lamb (Steak) 19.9g 0.8g 3.2g 475kJ (115kcal) Lobster 26.41 3.12 1.94 143 Milk (Whole) 3.3g 4.7g 3.6g 268kJ (64kcal) Orange 1.1g 8.5g 0.1g 167kJ (39kcal) Pasta 12.5g 73.0g 1.4g 1505kJ (355kcal) Peanut Butter (Crunchy) 24.9g 10.1g 50.2g 2452kJ

Peas 5.9g 9.0g 0.9g 290kJ (70kcal) Pork Chops 19.3g 20.3g 1080kJ (260kcal)

Porridge oats 11.0g 60g 8.0g 1500 kJ/ (356 kcal)

Potatoes 2.1g 17.2g 0.2g 335kJ (80kcal) Prawns 17.0g 0.3g 0.9g 330kJ (80kcal) Pumpkin Seeds 28.8g 15.2g 45.6g 2435kJ/586kcal Rice (brown) 6.9g 74.0g 2.8g 1480kJ (350kcal) Salmon Fish Fillets (Boneless) 21.6g 0g 14.0g 885kJ (215kcal)

Sardines (Fish) 21.5g trace 9.6g 721kJ (172kcal) Sausages (pork) 13.9g 11.9g 17.0g 1069kJ soya beans 35.9g 14.8g 18.6g 1555kJ (375kcal) Spaghetti 5.1g 33.0g 1.3g 700kJ (165kcal) Spinach 2.8g 1.5g 0.8g 103kJ (24kcal) Sunflower Seeds 23.4g 18.6g 47.5g 2475kJ (600kcal)


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Tilapia Fish 24g 0 4g 105 Tofu 12.1g 0.6g 6.0g 438/105 Tuna Fish (Steak) 25.6g 0g 0.5g 455kJ (110kcal) Tuna Fish (Tinned) 26.3g 0.0g 10.7g 843kJ / 202kcal

Turkey Breast (Skinless) 22.3g 0g 1.2g 425kJ (100kcal)

Yogurt 4.5g 6.6g 11.0g 600kJ (145kcal)

Source: www.howmuchprotein.com Are you building muscle? Are you into sport and need endurance? Do you want to lose weight? Do you want to increase your power and speed?

LECTURE 5: Factors leading to rancidity and reversion

Rancidity

When food containing fat and oil come in contact with surrounding oxygen and these auto oxidation leads to bad smell and change in taste, the whole process is said to be rancidity.

Mostly any food can technically become rancid. The term particularly applies to oils. Oils can be particularly susceptible to rancidity because their chemistry which makes them susceptible to oxygen damage.

Oxidation of fats is caused by a biochemical reaction between fats and oxygen. In this process long chain fatty acids are degraded and short chain compounds are formed. One of the reaction products is butyric acid, which causes the typical rancid taste.

Rancidification is the decomposition of fats, oils and other lipids by hydrolysis or oxidation, or both. Hydrolysis will split fatty acids chains away from the glycerol backbone in glycerides. These free fatty acids can then undergo further auto-oxidation. Oxidation primarily occurs with unsaturated fats by a free racial mediated process. These chemical processes can generate highly reactive molecules in rancid foods and oils, which are responsible for producing unpleasant and noxious odors. These chemical processes may also destroy nutrients in food. Under some conditions rancidity leads to destruction of vitamins in food.

Factors affecting rancidity and reversion.


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1. OXIDATION Oxygen is eight times more soluble in fats than in water and it is the

oxidation resulting from this exposure that is the primary cause of rancidity.

Oxidation primarily occurs with unsaturated fats by a free radical-mediated process.

These chemical processes can generate highly reactive molecules in rancid foods and oils, which are responsible for producing unpleasant and noxious odors and flavors. This process is called auto oxidation or oxidative rancidity.

2. HYDROLYSIS Triglycerides react with water under appropriate conditions to form

diglycerides and free fatty acid residues. Diglycerides later combine with water to form monoglycerides and fatty acids.

Finally the monoglycerides undergo completely hydrolysis to form glycerol and fatty acids. This process is called hydrolytic rancidity.

3. PRESENCE OF MICRO-ORGANISMS-MICROBIAL LIPASE Certain microorganisms can produce the hydrolytic enzyme called

lipase, which directly interferes the hydrolysis of triglycerides and produce glycerol and fatty acid. This fatty acids may undergo auto oxidation and become rancid.

The microbial lipase requires suitable pH and other conditions for its activity upon fats and oils.

4. PRESENCE OF UNSATURATION IN FATTY ACID CHAIN When a fatty substance is exposed to air, its unsaturated components

are converted into hydro peroxides, which break down into volatile aldehydes, esters, alcohols, ketones and hydrocarbons, some of which have disagreeable odors.

Butter becomes rancid by the above mentioned process and by hydrolysis, which liberates volatile and malodorous acids, particularly butyric acid.


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Saturated fats such as beef tallow are resistant to oxidation and become rancid at ordinary temperatures.

5. POLYUNSATURATION The more polyunsaturated a fat is, the faster it will go rancid.

Vegetable oils have to become several times more rancid than animal fats.

Presence of polyunsaturation in oils and fats makes them more susceptible to rancidity than monounsaturated and other types of unsaturated fatty acids.

6. CHEMICAL STRUCTURE OF OILS AND FATS. If the oils and fats are chemically more complex and consists more

number of double bond, more number of carboxyl/hydroxyl groups, then the chances of becoming rancid is high.

The double bonds found in fats and oils play a role in autoxidation. Oils with a high degree of unsaturation are most susceptible to

autoxidation. The best test for autoxidation is determination of the peroxide value.

Peroxides are intermediates in autoxidation reaction. The peroxide value of an oil or fat is used as a measurement of the

extent to which rancidity reactions have occurred during storage.

7. TEMPERATURE AND pH. These are the important factor which influences the food items rich in

fat and oils become rancid. Suitable temperature and alkaline pH are required for the hydrolytic

action of microbial lipase. Temperature and pH indirectly influence the autoxidation and

hydrolysis. 8. HEAT AND LIGHT

Presence of heat and light accelerate the rate of reaction of fats with oxygen, i.e. heat accelerates autoxidation.

Heat and light acts as the energy source for the production of free radical in rancidity and reversion of oils and fats.


22

LECTURE 6: Prevention of rancidity, commercial uses of fats and oils.

PREVENTION OF RANCIDITY

1. Addition of antioxidants The best method used to prevent food item from rancidity is the

addition of antioxidants. Antioxidants are added to fat containing foods in order to retard the

development of rancidity due to oxidation. There are five types of antioxidants

1)Natural antioxidants 2) Synthetic antioxidants 3) Semi synthetic antioxidants: Gallic acid, Propylagallate 4) Metal chelators: Citric acid, Phosphoric acid 5) Oxygen scavengers: Ascorbic acid

Natural anti-oxidants include flavonoids, polyphenols, ascorbic acid (vit C) and tocopherols(vit E).

Synthetic antioxidants include butylated hydroxyanisole(BHA), butylated hydroxytouluene(BHT), propyl 3, 4, 5-trihydroxybenzoate also known as propyl gallate and ethoxyquin.

The natural antioxidants tend to be short lived, but synthetic antioxidants give longer shelf life and better action.

The effectiveness of water soluble antioxidants is limited in preventing direct oxidation within fats, but is valuable in intercepting free radicals that travel through the watery parts of foods. A combination of water soluble and fat soluble antioxidants is ideal, usually in the ratio of fat to water.

2. Addition of sequestering agents These agents bind metals, thus preventing them from catalyzing

antioxidants. Examples of sequestering agents include EDTA and citric acid.

3. Proper storage of fats and oils.


23

Another method for preventing rancidity of food is the proper storage, keeping away the action of oxygen.

Rancidification can be decreased by storing fats and oils in a cool, dark place with little exposure to oxygen or free radicals, since heat and light accelerates the rate of reaction of fats with oxygen.

Do not add fresh oil to vessels containing old oil. The old oil will trigger a reaction and the new oil will become rancid if the oil was stored in a clean empty vessel.

Avoid using vessels that are wet, this will also speed up the problems associated with oxidation, allow tanks to drain and dry adequately before use.

COMMERCIAL USES OF FATS AND OILS.

Culinary uses-

Many vegetable oils are consumed directly, or used directly as ingredients in food- a role that they share with some animal fats, including butter and ghee.

The oils serve a number of purposes in this role: 1)shortening- to give pastries a crumbly texture. 2) texture- oils can serve to make other ingredients stick together less. 3) Flavor- oils such as olive oil or almond oil maybe chosen for the development of many food items. 4) Flavor base- oils can also “carry” flavors of other ingredients, since many flavors are present in chemicals that are soluble in oil.

Secondly, oils can be heated, and used to cook other foods. Oils that are suitable for this purpose must have a high flash point. Such oils include the major cooking oils- canola, safflower, peanut etc. some oils, including rice bran oil, are particularly valued in Asian cultures for high temperature cooking, because of their unusually high flash point.

Hydrogenated oils

Unsaturated vegetable fats and oils can be transformed through partial or complete hydrogenation into fats and oils of higher melting point. The hydrogenation process involves warming the oil at high temperature and pressure with hydrogen in presence catalyst such as nickel. As a result of hydrogenation the number of


24

double bond seceases and saturation increases. This may provide more resistance against rancidity (oxidation) or to change its physical characteristics.

Industrial uses

Vegetable oils are used as an ingredient or component in many manufactured products.

Many vegetable oils are used to make soaps, skin products, candles, perfumes and other personal care and cosmetic products.

Some oils are particularly suitable as drying agents, and are used in making paints and other wood treatment products.

Vegetable oils are used in the electrical industry as insulators as vegetable oils are non-toxic to the environment, biodegradable if spilled and have high flash and fire points. Tetra esters, an oil derivative generally have high stability to oxidation and have found its use as engine lubricants.

Commonvegetable oil has also been used experimentally as a cooling agent in PCs.

Vegetable oil is being used to produce bio-degradable hydraulic fluid and lubricant.

Vegetable based oils, like castor oil, have been used as medicine and as lubricants for a long time. Castor oil has numerous industrial uses, primarily due to the presence of hydroxyl groups on the fatty acid chains. Castor oil and other vegetable oils are important in the production of polyurethane plastic for many applications. These modified vegetable oilsare known as natural oil- polyols.

Pet food additive- Vegetable oil is used in production of some pet foods andVegetable oils which can be used as an effective food additive.

Fuel- production of biodiesel. Vegetable oils are also used to make biodiesel, which can be used like conventional diesel. Some vegetable oil blends are used in unmodified vehicles but straight vegetable oil needs specially prepared vehicles which have a method of heating the oil to reduce its viscosity. The vegetable oil economy is growing and the availability of the biodiesel around the world is increasing.

LECTURE 9: Properties of fluid foods


25

Viscosity: A fluid may be visualized as matter composed of different layers. Fluid moves if a force acts on it. The relative movement of one layer of fluid over another is due to the force called as shearing force. From Newton’s second law of motion, a resistance force is offered by the fluid to movement in the opposite direction to the shearing force. This resistance force is a measure of an important property of fluids called viscosity ‘’. Consider a deck of cards. A drag force is applied to the top layer of cards. The top card moves and the remaining cards move successively by layers with the bottom card remaining stationary. Now consider flow between two plates of infinite length. The bottom plate is fixed. Apply drag force to top plate. The top plate moves with a velocity dU. Bottom plate remains stationary. The remaining layers move successively by layers.

Figure 1: Fluid between two flat plates

Layers

Flat plate

Force Eeee


26

Figure 2: Velocity distribution and flow between two plates

Layers of fluid displaced

Flat plate Plate

Shearing force forrceForce Viscosity


27

The drag force depends on the frictional resistance offered by the surface between the layers of fluid.

dydU

t

dytdU

ThereforetdUx

Butdyx

ordyx

tan

dydU

SincedYdU

tLt

where µ is called absolute or dynamic viscosity.


28

The units of viscosity are: Poise, g/cm-s, Pa.s, kg/m-s and 0.01 poise = 1 cp (centipoises) Example: viscosity of water at ambient temperature is 1 cp viscosity of honey = 8880 cp

= kinematic viscosity

The units of kinematic viscosity are: m2/s Measurement of Viscosity: There are two types of viscometers namely the capillary tube viscometer and the rotational viscometer. Cannon-Fenske Capillary Tube Viscometer:


29

Figure 3: Capillary Tube Viscometer

Figure 4: Capillary tube The flow through the capillary tube is given by the following equation:

L

R


30

VtgR

tVQ

AVgP

ButQLPR

orL

PRQ

8

8

8

4

4

4

By measuring the length of time for liquid to drain from bulb, one can determine the viscosity of the liquid. Rotational Viscometer - Coaxial cylinder viscometer:

Figure 5: Coaxial cylinder viscometer Measure torque Ω required to turn inner cylinder at revolutions per unit time

L

Ro

Ri


31

ruLr

22

222

22

2

118

2

114

2

oi

i

oii

RRNL

NRRL

gIntegratindrdr

Lr

drdr

drdu

drdr

drdu

Effect of Temperature on Viscosity: The effect of temperature on viscosity is described by an Arrhenius type relationship

tGasconsREnergyActivationEonstArrheniuscB

where

TREB

g

a

A

Ag

aA

tan

lnln

Non-Newtonian Fluids: There are two types of Non-Newtonian fluids. 1. Time dependent (respond immediately with a flow as soon as a small amount of shear stress in applied) a) Rheopectic b) Thixotropic 2. Time independent a) HerschelBulkley


32

b) Bingham c) Dilatant (shear thickening) d) Pseudoplastic or power law (shear thinning) Apparent viscosity is calculated by assuming the Non-Newtonian fluid/liquid is obeying Newton’s law of viscosity. (Must be expressed along with the shear rate)

Figure 6: Shear Stress vs. Shear Rate Curves for Non-Newtonian Fluids

Shear thinning liquid – Viscosity decreases as shear rate increases Example: condensed milk, fruit purees, mustard, vegetable soups Shear thickening liquids – Viscosity increases as shear rate increases Example: 60% suspension of corn starch in water Bingham liquid – After a certain amount of yield stress, the liquid behaves as Newtonian Herschel Bulkley – After a certain amount of yield stress the liquid behaves as shear thinning liquid

Shear Stress

Shear Rate

Herschel-Bulkley

Bingham plastic

Pseudoplastic (shear thinning)

Newtonian

Dilatant (shear thickening)


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Models: Herschel Bulkley

n

o

o

n

drdU

PowerLawdydU

CassondydU

5.05.05.0

LECTURE 10: Properties of granular food and powders.

Food Rheology Consistency of flow under specified conditions Consistency / degree of fluidity and other mechanical properties are important since: - How long the food can be stored? - How stable it remains. - Determination of food texture. Acceptability of food is dependent upon – texture / spread-ability and creamy property. Food rheology is important for QC in food processing / manufacture - Rheological classification of food - solid, Gel, Liquid, Emulsion, Foam. -All these affect processing, shelf life, sensory (mouth feel) and appeal. Food Powders: Properties – Primary and Secondary

Particle - Primary Properties Particle - Secondary Properties

Shape Density

Settling velocity of particles Rehydration rate of powders Resistance of filter cakes

Primary properties of fluid: Viscosity


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Density Particle Size: Definition of particle: Common convention considers that a particulate material to be considered as a powder, it approximate median size should be <1mm. Coarse particles - Measure in cm/mm Fine particles - Measured in micrometers/nanometers

Median Particle Size in common food commodities Commodity BS Mesh Microns Rice & Barley 6-8 2800-2000 Granualated Sugar 30-34 500-355 Table Salt 52-72 300-210 Cocoa 200-300 75-35 Icing Sugar 350 45

Particle Shape: General Shapes of Particles: Shape Name

Shape Description Shape Name

Shape Description

Acicular Needle shape Flaky Plate like Angular Polyhedral

(roughly) Granular Approx.Equi-dimensional

irregular shape Crystalline Feely developed

shape in fluid medium

Irregular Lacks symmetry

Dentrite Branched crystalline

Modular Round

Fibrous Regular/irregular thread-like

Spherical Globe shape

Particle Density The bulk density, compressability and flowability of food powder are highly dependent on particle size and its distribution. Density = Total Mass / Total Volume Partticles possess: cracks/flaws/hollows/closed pores


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3 types of densities of particles: True density / Apparent Density / Effective

Density True Apparent Effective Mass / Volume –excluding open + closed pores + density of solid material of which the particle is made

Mass / Volume excluding only open pores

Mass / Vol. including open + closed pores

True density of many food powders is considerably lower than that of mineral or metallic powders Nonmetallic powders=<2000 kg/m3 Food Particles = 1000-1500 kg/m3

Measured by gas/liq. Displacement methods Liq or air pycnometers

Volume within the aerodynamic envelope Important in applications involving: Bulk flow air-fluidization Liq.-sedimentation Flow thru’ packed beds

Densities of common food powders Powder Density

kg/m3 Glucose 1560 Sucrose 1590 Starch 1500 Cellulose 1270-1610 Protein (globular)

~1400

Fat 900-950 Salt 2160 Citric acid 1540

The role, significance and sources of Microorganisms in foods Microorganisms are important food microbial germs found associated with foods. These are either the seeds of initial contamination of raw materials or contaminants due to handling and processing of such material, or microorganisms deliberately added for a technological purpose (in the case of lactic bacteria for example).

The importance of food microorganisms are represented primarily by four groups: bacteria, yeasts, molds and viruses.

Bacteria


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Among all the existing microorganisms, the bacteria that pose the greatest difficulty in preserving food. Most bacteria are relatively harmless, but they secrete enzymes capable of altering food. In some cases, bacteria can produce toxic substances.

Among thirty bacterial genera encountered on food, the most important are Escherichia, Salmonella, Pseudomonas, Bacillus, Clostridium, Lactobacillus and Staphylococcus. Some species such as Salmonella typhi, Staphylococcus aureus and Clostridium botulinum are pathogenic. Table 1 following lists the main bacterial genera encountered in foods

Table 1: Major bacterial genera encountered in food (the most common types).

Bacterial genera Food Example of pathogenic species Common Types Gram - Acinetobacter Meat

Alcaligenes Milk, poultry

Citrobacter (widespread)

Enterobacter (widespread)

Erwinia Fruits and vegetables

Escherichia (widespread)

Flavobacterium Fish, plants

Proteus Eggs, meat

Pseudomonas Milk, eggs, meat

Salmonella (widespread) Salmonella typhi Shigella (widespread) Shigella sonnei Vibrio Shellfish, fish Vibrio cholerae

Gram + Bacillus Meat, canned Bacillus cereus, B. anthracis Clostridium Meat, canned Clostridium botulinum, C. perfringens Corynebacterium (widespread) Corynebacterium diphtheriae Desulfotomaculum Canned

Lactobacillus Milk, meat

Micrococcus Milk, meat

Staphylococcus (widespread) Staphylococcus aureus Streptococcus (widespread) Streptococcus faecalis

Rare Types Gram - Acetobacter Beverages

Aeromonas Fish Aeromonas hydrophila Alteromonas fish


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Campylobacter Meat, milk Campylobacter jejuni Klebsiella (widespread) Klebsiella pneumoniae Moraxella Meat

Yersinia Meat Yersinia pestis, Y. parahaemolyticus Gram + Brochothrix Meat vacuum

Leuconostoc Milk, meat, beverages

Pediococcus Fermented foods

Sarcina Meat, sausages

Yeast Widespread in nature, particularly affect yeast acidic, sweet, salty or high in fat. They tolerate the cold better than heat, most yeasts are destroyed from 77 ° C.

Most yeasts encountered in food belong to the families of Saccharomycetaceae and Crytococcaceae. Table 2 below lists the main types of yeast found in foods.

In general, yeasts are not pathogenic. But their presence in foods is often undesirable because of deterioration that can result.

Table 2: Main types of yeast found in foods. Family Genre Food

Saccharomycetaceae Debaryomyces Charcuterie, wines, beverages Hansenula Fruit juices, pickles, mushrooms

Kluyveromyces Beverages Pichia Eggs

Saccharomyces Fruits, vegetables, beverages, eggs Saccharomycopsis Beverages, sauerkraut

Schizosaccharomyces Sugar products Crytococcaceae Brettanomyces Beer, acidified products

Candida Meat, margarine Kloecker Beverages Phaffia Beverages

Rhodotorula Beverages Trichosporon Meat, beer

Molds The molds are widespread in nature and are common in soil and dust in the air. When moisture conditions, aeration and temperature are right, mold can grow on almost all foods. The emergence of common tasks or greenish black bread provides a trivial example.

Molds are also able to survive in many other environments seem a priori against inappropriate to life. These are the concentrated solutions of acids, very dilute solutions of certain salts, glue, etc.. However, they can grow in the presence of oxygen.


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Molds grow very easily on walls and ceilings of buildings where high humidity is often the form of condensation. They even manage to grow in refrigerators because they tolerate cold better than heat.

Molds are also able to consume acids. Their presence in acidic foods can neutralize the acidity that normally prevents the development of Clostridium botulinum.

Several kinds of molds are found on foods, but the most common are: Aspergillus, Alternaria, Botrytis, Penicillium, Rhizopus and Mucor. They are found mainly in cereals and derivatives, dairy products, meats and cooked meats, oilseeds, fruits and vegetables, dried fruits, jams and beverages (Table 3). Some species are toxigenic, and they produce mycotoxins which ingestion of a sufficient quantity causes poisoning in consumers. However, the presence of a toxigenic species on a foodstuff does not necessarily mean that it is dangerous and it is necessary to investigate and determine the mycotoxins in food in order to confirm or affirm its safety. Indeed, the substrate and environmental conditions play an important role in the production of mycotoxins.

Table 3: Main types of molds found in foods. Genre Food Some toxigenic species

Aspergillus Rice, cereals, fruits, eggs, oils, cakes, peanuts, sugar cane

Aspergillus flavus, A. ochraceus, A.versicolor, A. clavatus

Botrytis Fruits and vegetables

Byssochlamys Canned fruits, beverages Byssochlamys nivea, B. fulva Cladosporium Prunes, meat, cereals, milk

Curvularia Copra, rice

Eurotium Cereals, meat

Fusarium Cereals, fruits and vegetables Fusarium moniliforme, F. oxysporum, F. graminearum

Geotrichum Oils, milk

Helminthosporium Rice plants

Mucor Dairy products, cereals, fruits, coconut, eggs

Penicillium Fruits, copra, cereals, rice, meat, eggs, milk

Penicillium citrinum, P. citreoviride, P. cyclopium, P. martensii, P. patulum, P. pubertum, P. expansum, P. viridicatum, P.islandicum, P. palitans, P. roqueforti, P. urticae, P. ochrosalmoneum, P. camemberti, P. paxilli, P. crustosum

Rhizopus Bread, fruit (strawberries, bananas, plums), copra, palm

Trichothecium Milk, fruits and vegetables

Viruses


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Viruses can reproduce only within a living cell. They parasitize both multicellular living beings (animals, plants) that unicellular (bacteria, etc.).. They are present in many food products. A distinction is made between specific bacterial viruses (bacteriophages) and infectious virus specific animal cells.

Bacteriophages attack the intestinal flora and cause disturbances more or less serious. They are found on foods that support a large number of bacteria-host. They are spread through fecal-oral route.

The infectious virus specific animal cells are found in certain foodstuffs and transmitted also by the fecal-oral. Examples of viruses: polio virus, the virus of hepatitis, echovirus, adenovirus, etc.

Sources Microorganisms are present in natural ecosystems such as air, soil and water. They are also present on the man himself and all living animals and plants. Therefore, all processed foods or can not be contaminated by microorganisms. Contamination of food may have a more or less serious about product quality and consumer health. It can cause a deterioration of the product, making it lose its organoleptic characteristics and / or business; sometimes cause food-poisoning or serious infections. The origin of the microorganisms found in foods depends on the one hand, the environment of the production of raw materials (soil, air, water) and on the other hand, requirements for its manipulation (crop or capture, transport, etc..) and processing (machinery, personnel, salaries of stabilization, etc..) in the finished product. Initial contamination of food by microorganisms in water The initial contamination of raw food is the product itself and the environment on which it was derived, namely water, soil and air. The water contains suspended diverse microbial load. The seeds are mostly water from the soil bacteria (Micrococcus, Pseudomonas, ...) or feces of human or animal (Enterobacteria, Enterococci, ...). These bacteria are often seeds of weathering and sometimes pathogenic to humans (Salmonella, Shigella, ...). Molds such as Aspergillus, Penicillium, Fusarium, may also be present in water, and are often seeds of adulteration of food. Yeasts, for against, are rarely encountered and therefore not involved in the contamination of food by microorganisms in the water. The food of marine origin may be contaminated by germs from seawater (Aeromonas, Bacillus, Pseudomonas, ...). Usually these microorganisms are not pathogens. However, they can cause alterations in the fish after capture. Contamination by soil microorganisms Given the interaction between water and soil, found in the microorganisms have been cited for water. However, the importance of Clostridium among soil bacteria.


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Products of plant origin (fruits, vegetables, etc..) Are most vulnerable to contamination by soil microorganisms. Contaminants can be transported by irrigation water, wind, insects and birds. Contamination by air microorganisms The air contains a large number of microbial cells. These are mostly bacteria, some fungi (Aspergillus, Alternaria, Penicillium, ...) and rarely yeasts. Bacteria encountered in the air are the Micrococcus spore and bacteria, and pathogens are generally absent. The most exposed to contamination by microorganisms in the air are those prepared in direct contact with air such as fruits, vegetables, meats, etc.. Contamination by microorganisms present on the products themselves There are two types of microorganisms naturally present in food: the surface of microorganisms and the microorganisms in the digestive tract of animals.

Surface microorganisms food

Animals and plants contain live on their surface (skin of animals, plants envelopes, eggshells, etc.). An important microorganisms. Under normal conditions, this surface acts as a barrier to the penetration of germs inside products. After the death of cells, the envelope no longer plays its role of protection because of the damage it has suffered, be it chemical, enzymatic or mechanical (cutting, grinding, pressing, etc.).. Thus, the products may be contaminated by microorganisms on their surface. The feed can also be contaminated by microorganisms on teats. Similarly, damaged fruit and vegetables following harvest operations are contaminated by germs that are naturally on the surface. Microorganisms found on the surface of foods are those usually encountered in soil, air and water. So these are bacteria (Micrococcus, Enterobacter, ...), molds (Aspergillus, Penicillium, Fusarium, ... ) and yeasts (Saccharomyces, ...).

Microorganisms in the digestive tract of animals

Microorganisms naturally present in the digestive system are usually bacteria such as Enterobacteria (Salmonella, Escherichia, Shigella, ...), enterococci (Streptococcus, ...) and other (Staphylococcus, Lactobacillus, ...). Molds are poorly represented among the yeasts, the genus Candida is the most common. The viscera are the main sources of contamination of meat and fish. The contamination of muscle tissue is by migration of microorganisms through the lymphatic system and is facilitated by cutting and washing of carcasses. Contamination by plant and its environment When performing the processing of food processing, these products are contaminated by microorganisms in the plant environment. Food products are again contaminated by germs from water, soil and air, plus other factors of contamination and that are unique to the plant (surfaces, equipment, utensils, personnel, etc. .).


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These contaminants cause the diversity of the microbial flora found on food, but still specific to each product for the physico-chemical properties they own. These characteristics have a decisive role on the development or inhibition of such specific microbial flora. Contamination by water Besides its use as an ingredient in food preparation, water is used in several food processes: washing, fluid transport, cooling, cleaning and disinfection, etc.. When the water is of poor microbiological quality, it is an important source of food contamination. Water cooling, for example, is responsible for most of the contamination of sterilized cans, but badly crimped. Contamination by air The air is again an important source of contamination of foods that are handled in the open air. Air filtration and work under controlled atmosphere, reduces the contamination of food by microorganisms in the air. Contamination by machinery and utensils Machinery (grinders, mixers, etc..) And utensils (knives, etc..) Are also an important source of food contamination during preparation. Germs carried by the equipment and utensils are generally the various contaminants of food. These bacteria multiply in the presence of food debris that remain adhered to the machines. That is why the plans for cleaning and disinfection of agro-industrial units should not be content with a superficial disinfection of equipment, but they must also provide for the dismantling of machinery and cleaning and disinfection of rooms, with sufficient frequency. Contamination by staff Contamination of foods during processing by staff is as important as the water contamination, air and machinery. Microorganisms transmitted by staff are those that exist naturally in the human body or which may come from contaminated raw materials that the staff handles. Also, it is important to note that staff may be an important source of fecal contaminants (Escherichia, Staphylococcus, ...). To control this type of contamination of food, it is essential that staff comply with good hygiene practices. Types of Microorganisms in Foods

1. Bacteria 2. Fungi 3. Protozoa 4. Viruses

1. Bacteria 2. Fungi 3. Protozoa 4. Viruses Lactic acid bacteria Acetic acid bacteria Propionic acid bacteria Butyric acid bacteria Proteolytic bacteria Lipolytic bacteria Saccharolytic bacteria Gas-producing bacteria Coliforms

• Eukaryotic organisms with rigid cell walls that lack chloroplasts

• Cell size: >10 μm • Three groups: yeasts,

molds and mushrooms

• Yeast: mostly unicellular

• Eukaryotic organisms without rigid cell walls that lack chloroplasts and are quite motile • Unicellular in at least one life stage • Cell size: >10 μm • Four groups: ciliates,

4. Viruses • Non-cellular genetic elements • Size = 0.1 μm • Obligate parasites • Replicates inside of the host’s cells by producing multiple viral particles


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• Molds: multi-cellular and differentiated filamentous Fungi

amoebas, flagellates and Sporozoa

1. Bacteria in Foods Acinetobacter Aeromonas Alcaligenes Arcobacter Bacillus Brochonthrix Campylobacter Carnobacterium Citrobacter Clostridium

Corynebacterium Enterobacter Enterococcus Erwinia Escherichia Flavobacterium Hafnia Kocuria Lactococcus Lactobacillus

Leuconostoc Listeria Micrococcus Moraxella Paenibacillus Pantoea Pediococcus Proteus Pseudomonas Pshychrobacter

Salmonella Serratia Shewanella Shigella Staphylococcus Streptococcus Vagococcus Vibrio Weissella Yersinia Xanthomonas

Molds in Foods Alternaria Aspergillus Aureobasidium Botrytis

Byssochlamys Cladosporium Colletotrichum Fusarium

Geotrichum Monilia Mucor Penicillum

Rhizopus Trichothecium Wallemia Xeromyces

Food Spoilage Bacteria Acinetobacter Alcaligenes Bacillus Brochonthrix Carnobacterium Citrobacter

Clostridium Corynebacterium Erwinia Flavobacterium Hafnia Kocuria

Lactococcus Lactobacillus Leuconostoc Moraxella Paenibacillus Pediococcus

Pseudomonas Pshychrobacter Shewanella Vibrio Xanthomonas

Sources of Microorganisms in Foods • Plants – Epiphytic flora – Plant pathogens – Soil microorganisms

• Animals – Skin, Hair, feathers, hooves, etc. – Intestinal tract – 1010 CFU/g feces - Pathogens are shed in feces

LECTURE NUMBER 8- BROWNING REACTIONS.

Food can be-

Naturally brown- eg. Sapota fruit. Expected to be brown- bread, coffee, cooked meat. Not expected to be brown- Fruits, vegetables.

There are three major types of browning reaction-

1. ENZYMATIC 2. NON-ENZYMATIC


43

3. CARAMELIZATION

I.ENZYMATIC

Occurs due to oxidation by oxidative enzymes on phenolic compounds (tannins, Leuco anthocyanin). When fruits get cut, the cell content comes in contact with air, the intracellular oxygen and phenolics gets oxidized giving the brown color. Phenolic oxidase is substrate specific only to certain phenolic compounds, thus only few fruits get browned. Eg.Apple, banana, brinjal, potato.

Phenolic compound + O2 (air+ intracellular) ------ Quinone (light brown)-----Dark Quinone phenol oxidase enzymepolymerised

The mechanism of this polymerization is unknown.

Prevention of enzymatic Browning Reaction-

1. Heating or blanching- Heating or blanching( cooking for short period) with no dissolved molecular oxygen. Enzymes get denatured.

2. Addition of salt- Vegetables immersed in salt NaCl with temperature, inhibits enzyme activity.

3. Lowering pH- 2.5 to 2.7 addition of ascorbic acid (vit c). Quinones formed are reduced to their dihydroxyl state by vit C. Vit C is oxidized to dihydroxy ascorbic acid.

4. Chilling below enzymatic activity- optimum temperature of enzyme activity is 43 degree C. Cold storage/ Frozen storage shows reduced browning.

II. NON-ENZYMATIC

Millard was the first person to discover browning cause owing to the presence of sugars and aminoacids in the food.

Millard reaction- carboxylamine reaction. Condensation of amino NH2 group + carboxyl group of sugar--------------------Brown pigment various reactions-Fragmentation, Polymerisation,rearrangement. Aroma/Flavor is affected. cereals ,toffees, bakery. Food product- Amino acid involved. Beer- glycine. Fresh Bread- Leucine. Maple syrup- Amino butyric acid.


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Features

Millard reaction desirable is cooking/baking. Undesirable browning in storage industry. Unpreventable but can be controlled. Both reactants carboxyl and amine present within food.

Conditions favoring millard reaction-

1. Presence of amino group- Pectins, peptides, amino acids. 2. Carboxyl groups- aldehydes, ketones. 3. Time, Moisture- 13% favors. Very high or very low decreases rate of reaction 4. pH -alkaline 7.8 suffers citrate/ acetate PO4) 5. Concentration of reactants (lysine favors millard reaction). 6. Temperature- increases with temperature. 7. Presence of catalyst- Cu, Fe.

Undesirable effects-

Off odor Off flavor- mild, stale, bitter. Off color- mild cream to nearly black.

Eg: dried milk powder, condensed milk, coconuts (saffron) Loss of nutritive value.

III. CARAMELIZATION

Formation of melanoidins by heating sugar to high temperature in low water(aprox 13%) presence.

No protein or nitrogenous compounds involved. Dehydration reaction resulting in polymerization. Sucrose ------------------caramel + acid.

at high temp decompostion, dehydration, polymerization.

Used to produce caramel colors/ Flavors.

Generic progression of reactions of caramelization.

heat at 160 degree C(14%H20) heat at 200 degree C(25 min, -4.5% H20)

Sucrose dispersed in small amount of water------------------- Crystals (molten)--------- C12H22O11


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Polymerized very light brown-----------CARAMELAN ( C22H36O18 )---- 55 min 200 degree 55 min 200 degree -9% water -14% water

CARAMELEN (C36H50O25)-----------CARAMELIN(C125H188080)

(darkest brown pigment)55min 200 degree (Black) Ascorbic acid browning.

Coccum Strawberry (crimson red) --------------------- fades to rusty brown. Squashes air (anthocyanin)

Ascorbic acid undergoes oxidation and oxidized product attributes to the brown pigmentation.

Factors leading to ascorbic acid browning-

Oxygen. Reducing sugar High pH. Warm storage conditions.

Prevention-

Freezing Addition of sodium sulphite. Freezing and Na2SO3 reduces reaction when required.

Lipid browning.

Amino groups of phospholipids+ lipoproteins.-------------------------------------------Brown color reaction with aldehydes+ reducing sugar

Features-

Quite uncommon. Can be seen, if kept for long time. It is an undesirable browning reaction. Eg: Milk, butter.

Detrimental effects of browning Enzymatic-Apples, bananas less appealing Millard reaction- Quick,toasted products, some lysine, methionine lost. Ascorbic-some Ascorbic acid is lost. Auto oxidation of vit C.


46

Lecture-16-17

MICROBIOLOGICAL EXAMINATION OF SURFACES

The need to maintain food contact surfaces in a hygienic state is of obvious importance. The primary problem that has has to be overcome when examining surfaces or utensils fo <r microorganisms is the removal of a significant percentage of the resident biota.

Although a method may not recover all organisms; its consistent use is specified areas of a food processing plant can still provide valuable information as long as it is realized that not all organisms are being recovered.

The most commonly used method for surface assessments in food operations are present below:

1. Swab/Swab-rinse Methods Oldest and most widely used method in food and dairy industries as well as in hospitals and

restaurants. The sterile template is placed over the surface, and the exposed area is rubbed thoroughly with a

moistened swab. The exposed swab is returned to a test tube containing a suitable diluent and stored at refrigerator

temperatures until plated. Swabs may be cotton or calcium alginate swab. When cotton swab is used, the organism must be dislodged from the fibers. When calcium alginate swabs are used, the organisms are released into the diluent upon dissolution

of the alginate by sodium hexametaphosphate. Advantages of swab rinsed method-

The swab method is best suited for flexible, uneven, and heavily contaminated surfaces. The ease of removal of organisms depends on the texture of the surface and the nature and types of

biota. The swab-rinse method remains a rapid, simple and inexpensive way to assess the microbiological biota of food surfaces and utensils.

2. Contact Plate- Replicate Organism Direct Agar Contact (RODAC)

Introduced by Gunderson and Gunderson in 1945 RODAC method employs special petri plates, which are poured with 15.5-16.5 ml of an appropriate

plating medium, resulting in a raised agar surface. When the plate is inverted, the hardened agar makes direct contact with the surface. Surfaces are examined that have been cleaned with certain detergents, it is necessary to include a

neutralizer (tween 80, lecithin etc) in the medium. Once exposed, plates are covered and incubated, and the colonies enumerated. Advantages of RODAC-

The RODAC plate has been shown to be the method of choice when the surfaces to be examined are smooth, firm and non-porous.

Disadvantages of RODAC-


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Covering of agar surface by spreading colonies and its ineffectiveness for heavily contaminated surfaces.

This can be minimized by using plates with dried agar surfaces and by using selective media. 3. Agar Syringe/”Agar Sausage” Method

100 ml syringe is modified by removing the needle end to create a hollow cylinder that is filled with agar.

A layer of agar is pushed beyond the end of the barrel by means of the plunger and pressed against the surfaces to be examined.

The exposed layer is cut off and placed in a petri dish, followed by incubation and colony enumeration.

4. Other surface methods.

a) Direct surface A number of workers have employed direct surface agar plating methods, in which melted agar

is poured onto the surface or utensil to be assessed. Upon hardening, the agar mold is placed in a petri dish and incubated. It was used successfully to determine the survival of clostridium sporogenes on a stainless steel

surfaces. Although effective as a research tool, the method does not lend itself to routine use for food

plant surfaces. b) Sticky Film It consists of pressing sticky film or tape against the surface to be examined and pressing the

exposed side on an agar plate. It was shown less effective than swabs in recovering bacteria from wooden surfaces.

c) Swab/Agar slant Sampling with cotton swabs that are transferred directly to slants. Following incubation, slants are grouped into one-half log 10 units based on estimated numbers

of developed colonies. The avg number of colonies is determined by plotting the distribution on probability paper. d) Ultrasonic Devices Ultrasonic devices have been used to assess the microbiological contamination of surfaces, but

the surfaces to be examined must be small in size and removable so that they can be placed inside a container immersed in diluent.

Once the container in an ultrasonic apparatus, the energy generated effects the release of micro-organisms into the diluent.

e) Spray gun This method involves the impingement of a spray of washing soln against a specific area of

surface and subsequent plating of the washing soln. Although the device is portable, a source of air pressure is necessary. Much more effective than swab method in removing bacteria from meat surfaces.

AIR SAMPLING

Air is not a suitable medium for the growth of micro-organisms but it contains large number of aerosols, droplets and droplet nuclei which may contribute a significant contamination of food.


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A variety of methods are used for the sampling of air in food plants for the presence and relative number of micro-org.

The most imp methods are- a) Impingement in liquid b) Imrpaction on solid surface c) Filtration d) Sedimentation e) Centrifugation f) Electrostatic precipitation g) Thermal precipitation

Most commonly used methods are sedimentation, impaction and impingement. One of the simplest methods of air sampling is to open prepoured petridishes for specific

periods of time in the area to be assed. The most imp factors influencing this method are the size of the particle and the flow speed of

air current. If the agar surface is exposed for too long, drying will affect the growth of the micro-org. The presence and relative number of different types of organisms can be assessed using

appropriate selective media. Two popular air samplers- glass impinge and the Anderson sieve sampler. They have the

advantage that a specific volume of air can be sampled. In glass impinger, a specific quantity of dilutents is placed in the impinger and air is pulled by

vacuum through a capillary orifice with the air impinging on the diluent, where micro-org are trapped in the liquid.

The sample may then be plated by use of selective media or SPC. In Anderson air sampler, air is drawn through one or more sieves and the micro-org are trapped

on the surface.

MICROBIOLOGICALLY INJURED ORGANISMS.

When micro-org are subjected to environmental stresses such as lethal heat and freezing, many of the individual cells undergo metabolic injury, resulting in their inability to form colonies on selective media that uninjured cells can tolerate.

Whether a culture has suffered metabolic injury can be determined by plating aliquots separately on a non selective and a selective medium and enumerating the colonies that develop after suitable incubation.

The colonies that develop on the nonselective medium represent both injured and uninjured cells, whereas only uninjured cells develop on the selective media.

The difference between the no. of colonies on the two media is the measure of the no. of injured cells in the original culture or population.

Injury of food borne micro-org has been shown not only by sub-lethel heat and freezing but also by freeze drying, drying, irradiation, aerosolization, dyes, sodium azide, salts, heavy metals, antibiotics, essential oils, and other chemicals such as EDTA and sanitizing compounds.

These organisms may also be injured via increased lag phases of growth, increased sensitivity to a variety of selective media agents, damage to cell membranes and TCA-cycle


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enzymes, breakdown of ribosomes and DNA damage.

Detection of Microorganisms in Food

Enumeration Detection Viabl e+ Total Physical Chemical Immunological 1. Standard Plate Counts (SPC) 2. The Spiral Plater 3. Membrane - DEFT - Microcolony DEFT - HGMF

4. Microcolony 5. MPN 6. Dye Reduction

Calorimetry Impedence

Litmus Lysate FAT RIA Hemoagglutination

The 4 basic methods employed for "total" numbers are as follows:

1. Standard plate counts (SPC) for viable cells

2. The Most Probable Numbers (MPN) method as a statistical determination of viable cells

3. Dye reduction techniques to estimate number of viable cells that possess reducing capacities

4. Direct microscopic counts (DMC) for both viable and nonviable cells

1. Standard plate counts (SPC) for viable cells

By the conventional SPC method, portions of food samples are blended or homogenized, serially diluted in appropriate diluents, plated in or onto a suitable agar medium, and incubated at an appropriate temperature for a given time, after which all visible colonies are counted by use of a Quebec or electronic counter.

Most widely used method for determining the numbers of viable cells or colony-forming units (cfu) in a food product.

Total viable counts should be viewed as a function of the following factors:

• Sampling methods employed

• Distribution of the organisms in the food sample

• Nature of the food biota

• Nature of the food material

• The pre-examination history of the food product

• Nutritional adequacy of the plating medium employed

• Incubation temperature and time used

• pH, water activity (aw), and oxidation-reduction potential (Eh) of the plating medium


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• Type of diluents used

• Relative number of organisms in food sample

Surface Plating: In this method, pre-poured and hardened agar plates with dry surfaces are employed. The diluted specimens are planted onto the surface of replicate plates, and, with the aid of bent glass rods, the inoculums is carefully and evenly distributed over the entire surface.

Surface plating offers advantages in determining the numbers of heat-sensitive psychrotrophs in a food product because the organisms do not come in contact with melted agar.

It is the method of choice when the colonial features of a colony are important to its presumptive identification and for most selective media.

Aerobes are favored by surface plating Disadvantages of surface plating:

The problem of spreaders (especially when the agar surface is not adequately dry prior to plating) The crowding of colonies, which makes enumeration more difficult

Homogenization of Food Samples: Microorganisms were extracted from food specimens for plating almost universally by use of mechanical blenders. Stomacher was developed by Sharpe and Jackson. The Stomacher, a relatively simple device, homogenizes specimens in a special plastic bag by the vigorous pounding of two paddles. The pounding effects the shearing of food specimens, and micro-organisms are released into the diluent. The Stomacher was shown to be less lethal than a blender to Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli. Significantly higher counts of Gram-negative bacteria were obtained by Stomacher

Key Benefits of Stomacher

disposable bag eliminates cleaning no sterilization of component parts require rapid and continuous throughput of samples minimal maintenance ideal recovery of bacteria minimal temperature rise of sample no aerosol released during blending bag can be heat sealed for toxic waste

2. The Spiral Plater

The spiral plater is a mechanical device that distributes the liquid inoculum on the surface of a rotating plate containing a suitable poured and hardened agar medium. The dispensing arm moves from the near center of the plate toward the outside, depositing the sample in an Archimedes spiral.


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The attached special syringe dispenses a continuously decreasing volume of sample so that a concentration range of up to 10,000:1 is effected on a single plate. Following incubation at an appropriate temperature, colony development reveals a higher density of deposited cells near the center of the plate, with progressively fewer towards the edge, since the concentration of the inoculums is highest at the centre and decreases towards the edge.

The enumeration of colonies on plates prepared with a spiral plater is achieved by use of a special counting grid. Depending on the relative density of colonies, colonies that appear in one or more specific areas of the superimposed grid are counted.

Advantages of Spiral Plater Disadvantages of Spiral Plater Less agar is used Fewer plates, dilution blanks, and pipettes are required Three to four times more samples per hour can be

examined. Only one plate is required for enumeration of a single

sample, unlike MPN tests where several tubes are required for dilution and enumeration.

Sample volumes of as low as 0.0018ml also give very effective results.

50-60 plates per hour can be prepared, and little training is required for its operation.

Food particles may cause blocking in the dispensing stylus.

It is more suited for use with liquid foods such as milk.

3. Membrane Filter Techniques Membranes with a pore size that will retain bacteria but allow water or diluents to pass are used.

Cellulose filters were among the earliest used; however, polycarbonate Nucleopore filters offer the advantage of retaining all bacteria on top of the filter.

a. Direct Epifluorescent Filter Technique: The direct epifluorescent filter technique (DEFT) employs fluorescent dyes and fluorescent microscopy, and it is a rapid technique for microorganisms in foods.

Typically, a diluted food homogenate is filtered through a 5µm nylon filter

The filtrate is collected and treated with 2 mL of Triton X-IOO and 0.5 mL of trypsin

After incubation, the treated fitrate is passed through a 0.6µm Nucleopore polycarbonate membrane, and the filter is stained with acridine orange

After drying, the stained cells are enumerated by epifluorescence microscopy, and the number of cells per gram is calculated by multiplying the average number per field by the microscope factor.

Application of DEFT: DEFT has been employed successfully to estimate numbers of microorganisms on meat and poultry and on food contact surfaces.

b. Microcolony-DEFT: DEFT allows for the direct microscopic determination of cells; microcolony-DEFT is a variation that allows one to determine viable cells only.


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Food homogenates filtered through DEFT membranes

Membranes placed on the surface of appropriate culture media

Incubated for microcolony development: 3-hour incubation for gram –ve bacteria; 6-hour incubation for gram+ve bacteria.

The microcolonies that develop viewed with a microscope.

For coli-forms, pseudomonads, and staphylococci, as few as 103/g could be detected within 8 hours. c. Hydrophobic Grid Membrane Filter: The hydrophobic grid membrane filter (HGMF)

technique was advanced by Sharpe and Michaud, and is used to enumerate microorganisms from a variety of food products. The method employs a specially constructed filter that consists of 1,600 wax grids on a single membrane filter that restricts growth and colony size to individual grids. On one filter, from 10 to 9 x 104 cells can be enumerated by an MPN procedure, and enumeration can be automated. The method can detect as few as 10 cells per gram, and results can be achieved in 24 hours or so. 1 ml of a 1:10 homogenate filtered through a filter membrane

Membrane placed on a suitable agar medium for incubation overnight

Colonies are allowed to develop; The grids colonies are enumerated, and the MPN (Most Probable Number) is calculated.

4. Microscope Colony Counts These methods involve the counting of microcolonies that develop in agar layered over microscope slides.

Microcolonies developed on agar layered over microscope slide

0.1ml of milk-agar mixture is taken

Spread over 4 cm2 area of glass slide

The plates are incubated at 370C for 3-8 hrs

The plates are then stained with thionin blue

Viewed under 16mm objective

Note: General, selective, and/or differential media can be used

5. Most Probable Number (MPN)


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In this method, dilutions of food samples are prepared as for the SPC. Three serial aliquots or dilutions are then planted into 9 or 15 tubes of appropriate medium for the three- or five-tube method, respectively. Numbers of organisms in the original sample are determined by use of standard MPN tables. The method is statistical in nature, and MPN results are generally higher than SPC results. This method was introduced by Mc Crady in 1915. When a three-tube test is used, 20 of the 62 possible test combinations account for 99% of all results, whereas with the five-tube test, 49 of the possible 214 combinations, account for 99% of all results.

Advantages of MPN Disadvantages of Spiral Plater It is relatively simple. Results from one laboratory are more likely to agree with those from another laboratory. Specific groups of organisms can be determined by use of appropriate selective and differential media. It is the method of choice for determining fecal coliform densities.

Large volume of glassware is required The colony morphology cannot be

observation The method lacks precision

6. Dye Reduction Techniques

Two dyes are commonly employed in this procedure to estimate the number of viable organisms in suitable products: methylene blue and resazurin.To conduct a dye-reduction test; properly prepared supernatants of foods are added to standard solutions of either dye.

Methylene Blue Reduction Test: In this method, Methylene blue dye is used to detect microbes in food homogenates/samples, mostly milk. The dye is blue in its oxidized state and turns white when reduced.

The dye is prepared by adding 1mg MB in 250ml Distilled water

10ml milk sample + 1ML OF Methylene blue, stoppered and mixed gently and then Incubated at 370C for 6 hours Resazurin Test: It is a rapid method for assessing ground beef spoilage. The dye is slate blue when oxidized and turns to pink or white when it is reduced.

Food samples are evaluated by resazurin reduction by adding 20 mL of a 0.0001% resazurin solution to 100 g of sliced meat in a plastic pouch. Advantages:-

i. they are simple, rapid, and inexpensive ii. only viable cells actively reduce the dyes

Disadvantages:-


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i. Not all organisms reduce the dyes equally ii. They are not applicable to food specimens that contain reductive enzymes unless special

steps are employed.

Time (min) Quality Bacterial numbers 0-30 Very poor 2×107 31-120 Poor 4×106 121-360 Fair 5×105 361-480 Good <5×105

Table:-Standards used in Dye Reduction Technique

food biotechnology notes

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